U.S. patent number 4,909,710 [Application Number 07/425,473] was granted by the patent office on 1990-03-20 for linear peristaltic pump.
This patent grant is currently assigned to Fisher Scientific Company. Invention is credited to David Burkett, David E. Kaplan, Laurence Warden.
United States Patent |
4,909,710 |
Kaplan , et al. |
March 20, 1990 |
Linear peristaltic pump
Abstract
A linear peristaltic pump equipped with a pressure relief
mechanism for pumping I.V. fluids to a patient comprises a platen
for supporting the tube, and a plurality of fingers which
sequentially urge against the tube resting against the platen for
creating a moving zone of occlusion. Cam lobes are formed to lift a
penultimate and ultimate finger off of the tube at a rate faster
than the other fingers to prevent pressure increases inside the
tube which would otherwise be caused by other fingers urging
against the tube. Additionally, the ultimate finger may be
shortened with respect to the other fingers to reduce the total
occlusion time of the ultimate finger to provide a more linearized
flow of fluid to the patient.
Inventors: |
Kaplan; David E. (Moraga,
CA), Burkett; David (Jonesboro, GA), Warden; Laurence
(San Diego, CA) |
Assignee: |
Fisher Scientific Company
(Pittsburgh, PA)
|
Family
ID: |
23686718 |
Appl.
No.: |
07/425,473 |
Filed: |
October 23, 1989 |
Current U.S.
Class: |
417/53; 417/474;
604/153 |
Current CPC
Class: |
A61M
5/14228 (20130101); F04B 43/082 (20130101) |
Current International
Class: |
F04B
43/00 (20060101); F04B 43/08 (20060101); F04B
043/12 () |
Field of
Search: |
;417/53,474,475,478,479
;604/153 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Smith; Leonard E.
Assistant Examiner: Szczecina, Jr.; Eugene L.
Attorney, Agent or Firm: Nydegger & Harshman
Claims
We claim:
1. A linear peristaltic pump for creating a moving zone of
occlusion along a resilient tube to pump fluid through the tube
which comprises:
a casing;
a platen for supporting the tube in a substantially linear
orientation;
a camshaft mounted on said casing, said camshaft having a series of
cam lobes each eccentrically mounted on said camshaft to establish
a helical series therealong, the penultimate and ultimate cam lobes
of said series each being formed with a flat;
a plurality of fingers each operatively engaged with one of said
respective cam lobes; and
means for rotating said camshaft to produce a reciprocal movement
of said fingers to sequentially urge said fingers against said tube
and control the occlusion created by said fingers engaged with said
penultimate and said ultimate cam lobes according to the location
of said flat.
2. A linear peristaltic pump as recited in claim 1 wherein said
menas for rotating said camshaft comprises a motor operatively
coupled to said camshaft and fixedly mounted on said casing.
3. A linear peristaltic pump as recited in claim 2 wherein said
casing has formed therein a plurality of internal grooves for
receiving said plurality of fingers therein to constrain said
fingers in said reciprocal movement.
4. A linear peristaltic pump as recited in claim 3 wherein said
camshaft rotates about an axis substantially parallel to the
tube.
5. A linear peristaltic pump as recited in claim 4 wherein said
flats on said penultimate cam lobe and on said ultimate cam lobe
are configured to lift said penultimate finger and said ultimate
finger from the tube at a rate faster than the rate at which the
other said fingers are lifted from the tube.
6. A linear peristaltic pump as recited in claim 5 wherein said
flat of said ultimate cam lobe is formed to shorten the reciprocal
movement of said finger in the direction of the tube.
7. A linear peristaltic pump as recited in claim 5 further
comprising an ultimate finger operatively engaged with said
ultimate cam lobe, said ultimate finger having a length shorter
than each of said plurality of fingers.
8. A linear peristaltic pump for creating a moving zone of
occlusion along a resilient tube for pumping fluid through the tube
which comprises:
a casing;
a platen for supporting said tube in substantially a linear
orientation;
a plurality of fingers slidably mounted within said casing, said
fingers serially aligned along the tube;
means for reciprocally moving said fingers to sequentially urge
said fingers against the tube; and
means for lifting said penultimate finger and said ultimate finger
from the tube at a rate faster than the rate at which the other of
said fingers are lifted from the tube.
9. A linear peristaltic pump as recited in claim 8 wherein said
means for reciprocally moving said fingers comprises:
a camshaft rotatably mounted on said casing;
a plurality of cam lobes eccentrically mounted on said camshaft to
establish a helical series therealong for operable engagement with
said plurality of fingers; and
a motor fixedly mounted to said casing and coupled to said camshaft
for rotating said camshaft.
10. A linear peristaltic pump as recited in claim 9 wherein said
camshaft rotates about an axis substantially parallel to the
tube.
11. A linear peristaltic pump as recited in claim 10 wherein said
casing has formed therein a plurality of grooves for receiving said
plurality of fingers therein to constrain said fingers for linear
reciprocal movement.
12. A linear peristaltic pump as recited in claim 11 wherein said
means for lifting said penultimate finger and said ultimate finger
from said tube comprises a flat formed on said penultimate cam lobe
and on said ultimate cam lobe.
13. A linear peristaltic pump as recited in claim 12 wherein said
flat is integrally formed on the circumference of said cam
lobe.
14. A linear peristaltic pump as recited in claim 13 wherein said
flat on said ultimate cam lobe shortens the reciprocal movement of
said finger in the direction of the tube.
15. A linear peristaltic pump as recited in claim 11 wherein said
ultimate finger has a length shorter than that of the other
plurality of fingers.
16. A method for linearizing fluid flow through a resilient tube in
a linear peristaltic pump which pumps I.V. fluids with a series of
fingers including a penultimate finger, an ultimate finger, and
other fingers comprising the steps of:
(A) Sequentially occluding a tube in wavelike fashion with said
series of fingers to create a moving zone of occlusion along said
tube;
(B) Disengaging said penultimate finger from said tube at a rate
faster than that of said other fingers;
(C) Occluding the tube with said ultimate finger for a shorter
period of time than that of said other fingers; and
(C) Disengaging said ultimate finger from said tube at a rate
faster than that of said other fingers.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to peristaltic pumps which
are used to pump fluid through resilient tubes. More particularly,
the present invention relates to the drive mechanism of a linear
peristaltic pump which minimizes the pulsatile effects of
peristaltic pumps. The present invention is particularly, but not
exclusively, useful in the health care field for the intravenous
administration of medical solutions to patients.
DISCUSSION OF THE PRIOR ART
Several pumps have been proposed which are specifically and
uniquely designed for intravenous (I.V.) infusion of medical
solutions to patients. The objective in each instance is to provide
a pump which can reliably and accurately control the flow of fluid
to the patient. Of the many types of pumps used for I.V. infusion,
the present invention is concerned with that type which exerts a
peristaltic action on the tube through which the fluid is being
pumped. Specifically, the present invention is concerned with pumps
which fall generally into the category of linear peristaltic
pumps.
Although the actual design for a linear peristaltic pump will
differ from pump to pump, linear peristaltic pumps generally
require the mechanical interaction of the following basic elements:
a platen; a resilient tube through which fluid is to be pumped
which rests against the platen; a peristaltic mechanism (i.e.
structure capable of creating a moving zone of occlusion along the
tube); and a driven mechanism for the peristaltic mechanism. The
peristaltic mechanism must operatively engage the I.V. tubing
through which the medical solutions are to be pumped. As is well
known by the skilled artisan, this engagement requires positioning
of the tube between the platen and the peristaltic mechanism.
It should be apparent that for a moving zone of occlusion to be
generated along the tube, the pump must squeeze the tube in some
sequential manner. This squeezing action occurs as the result of
relative movement between the peristaltic mechanism and the platen
to correspondingly generate a force to squeeze fluid through the
resilient tube. Problems arise in linear peristaltic pumps when the
occlusion on the tube causes short term deformation of the tube, or
allows excessive pressure to build up within the tube. This results
in uncontrolled variations in fluid flow through the tube, and thus
unwanted pulsatile flow, rather than the desired linear flow.
Some of the problems associated with a pulsatile flow of fluid can
be alleviated by increasing the number of fingers making sequential
contact with the tube. It has been found that the flow of fluid in
a linear peristaltic pump becomes noticeably more linear in nature
when the number of fingers exceeds eight (8). For practical
purposes, it has been found that the number of fingers should range
between eleven (11) and fourteen (14) to obtain the optimal linear
pumping arrangement.
There are additional problems, however, associated with even an
optimal number of fingers. Assuming for the moment that twelve (12)
fingers are optimal for the operation of a linear peristaltic pump,
during each cycle the first finger throug the twelfth finger will
sequentially occlude the tube in a wave-like action to cause fluid
flow through the tube. At the end of each cycle, the twelfth finger
will be causing the tube to occlude. As the next cycle begins,
there will be an interval in time during which the first finger
will also be occluding the tube. During this interval of time,
fluid is trapped between these two (2) points of occlusion (i.e.
the first and twelfth finger) to create a pocket of fluid within
the tube. While this pocket exists, the second, third and possibly
subsequent fingers are also in the process of urging against the
tube forming the pocket as they approach their respective points of
occlusion on the tube. This causes the pressure to increase
disproportionately in the pocket with respect to the downstream
fluid pressure. Consequently, when the twelfth finger lifts off the
tube to end the previous cycle, the balloon pressure created by the
second and third fingers against the pocket causes fluid to surge
from the pocket into the downstream tube. The result is a
non-linear or pulsatile flow of fluid into the patient.
The present invention recognizes that the lift-off sequence of the
peristaltic fingers (i.e. the sequence in which each finger starts
or stops occluding the tube) can be varied in their relation to
each other to provide a more uniform and less pulsatile fluid flow.
Specifically, the present invention recognizes that the camming
mechanism of a linear peristaltic pump can be set to establish a
predictable response for the sequencing of individual finger
occlusions which will tend to minimize surges in the resulting
fluid flow through the tube.
In light of the above, the present invention recognizes the need
for peristaltic pumps which are capable of continuously pumping
fluid through a resilient tube while minimizing any pulsatile
characteristics in the flow of fluid. Another object of the present
invention is to provide a linear peristaltic pump which minimizes
any fluid pressure changes in the fluid tube that can cause pulses
or surges in fluid flow through the tube. Yet another object of the
present invention is to provide a linear peristaltic pump which is
easy to manufacture and relatively simple to operate. Yet another
object of the present invention is to provide a durable and
reliable peristaltic pump which is cost effective and which
accurately infuses fluids to patients.
SUMMARY OF THE INVENTION
The preferred embodiment of the linear peristaltic pump having a
pressure relief mechanism of the present invention comprises a
plurality of fingers which press against an I.V. tube resting
against a platen. Specifically, the plurality of fingers
sequentially urge against the tube in wavelike fashion to create a
moving of zone of occlusion along the tube for forcing fluids
through the I.V. tube. The fingers are slidably housed inside a
casing to guide the reciprocal movement of the fingers.
The fingers are operatively coupled to a camshaft which selectively
controls the reciprocal displacement of each finger. Specifically,
the camshaft has a plurality of cam lobes spaced in a helical
relationship therealong to selectively move each respective finger
between an open or up position and a closed or down position.
Further, the camshaft is housed inside the casing and is connected
to a motor for providing the necessary rotational movement.
In its operation, the penultimate and the ultimate fingers (i.e.
the next-to-last and the last downstream fingers, respectively) are
lifted off the tube at a rate which is different than the rate at
which other fingers in the peristaltic mechanism lift off from the
tube. This is done to compensate for the increase in pressure
created by the downward movement of other fingers as they
subsequently begin to pinch the tube when both the first and
ultimate fingers are occluding the tube.
Stated differently, there are two (2) cooperative functions which
take place simultaneously to minimize the discontinuity in fluid
flow which occurs while the ultimate finger occludes the tube.
Firstly, the time is shortened during which the ultimate finger
occludes the tube. Secondly, while the ultimate finger and the
first upstream finger are occluding the tube, the penultimate
finger is lifting off the tube at a rate which compensates for the
urging of other fingers against the tube. This is done to equalize
fluid pressure in the pocket formed between the first upstream
finger and the ultimate finger.
Additionally, the help reduce the pressure build up inside the tube
when there are two (2) points of occlusion, the ultimate finger may
be shortened with respect to the other fingers by approximately one
hundredth of an inch (0.01") to reduce the total occlusion time of
the ultimate finger. This correspondingly increases the occlusion
time of the first finger. Obviously, the shortening of the last
finger can be accomplished by either modification of its
corresponding cam lobe or by actually reducing the length of the
finger.
The novel features of this invention, as well as the invention
itself, both as to its structure and its operation, will be best
understood from the accompanying drawings, taken in conjunction
with the accompanying description, in which similar reference
characters refer to similar parts, and in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front elevational view of a linear peristaltic pump
incorporating the peristaltic mechanism shown in its working
environment;
FIG. 2 is a cross-sectional view of the peristaltic mechanism
showing the plurality of fingers as seen along line 2--2 in FIG.
1;
FIG. 3 is a cross-sectional view of a finger operatively connected
to a cam lobe;
FIGS. 4A, 4B and 4C are cross-sectional views of cam lobes showing
various configurations which correspondingly control the reciprocal
movement of their associated fingers; and
FIG. 5 is a graph showing the percent occlusion of the tube by the
relative fingers with respect to time.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring initially to FIG. 1, a pump generally designated 10 is
shown in its intended environment. The pump 10 is mounted on I.V.
pole 12 in a manner well known in the art. An I.V. fluid source 14
is suspended from the I.V. pole 12 as shown in FIG. 1 and an I.V.
tube 16 is connected in fluid communication with fluid source 14
and operatively connected with pump 10 in a manner as generally
shown in FIG. 1. Tube section 18 of tube 16 is that portion of the
tube operatively engaged by the pump 10. I.V. tube 16 is
subsequently coupled to patient 20 for the infusion of fluid source
14 to patient 20.
FIG. 2 is a cross-sectional view of the peristaltic mechanism,
generally designated 22, which is shown here in isolation from pump
10 for purposes of clarity. As shown in FIG. 2, peristaltic
mechanism 22 includes a motor 24 which is preferably a stepper
motor but may be of any type well known in the relevant art. A
drive shaft 26 is rotated by the motor 24 and is secured to an
attachment 28 by any means well known in the art in a manner which
permits the rotation of attachment 28 to move a drive pulley 30.
Drive pulley 30 is connected in operative engagement with an
attachment 32 that is in turn secured to camshaft 34 by any means
well known in the art. Camshaft 34 is supported on peristaltic
mechanism 22 by a bushing 36 and a bushing 38. As can be
appreciated, bushings 36 and 38 are mounted within a casing 46.
Integrally connected onto camshaft 34 at predetermined locations
along the axis of the camshaft 34 is a series of cam lobes 40. As
will be appreciated by those skilled in the pertinent art, cam
lobes 40 are eccentrically mounted on camshaft 34 in a helical
pattern along the axis of camshaft 34 and are engaged with finger
42 in a manner which creates a wave-like movement of fingers
generally designated as 42 when camshaft 34 is rotated. Within the
mechanism, the plurality of fingers 42 includes a penultimate
finger 68 and an ultimate finger 70 which are operatively coupled
to a corresponding penultimate cam lobe 72 and an ultimate cam lobe
74. In addition, for the embodiment described herein, there are
also included a first finger 63, a second finger 65, and a third
finger 67. The movement of the plurality of fingers 42, which
includes both the penultimate finger 68 and ultimate finger 70,
will best be appreciated by reference to FIG. 3. For the moment,
however, all fingers and cam lobes wil be referred to generally as
42 and 40, respectively, for simplicity.
Referring to FIG. 3, it is seen that each of the individual fingers
42 are formed with an aperture 56 to receive the individual cam
lobe 40 therein. Each finger 42 is mounted in casing 46 of the
peristaltic mechanism 22 for movement in a direction substantially
perpendicular to the longitudinal axis of camshaft 34. To
accomplish this, the casing 46 has a side 48a and a side 48b which
are formed with baffles 50a and 50b that create grooves 52a and 52b
for maintaining the alignment of each respetive finger 42 relative
to camshaft 34. The rotation of camshaft 34 rotates each
eccentrically mounted cam lobe 40 so that it is urged against
respective wall portions 57 of the aperture 56 to cause a
reciprocal motion of finger 42 within the casing 46.
Referring again to FIG. 2, it can be appreciated by the skilled
artisan that cam lobes 40 can be located along camshaft 34 in a
helical manner. With cam lobes 40 so located, rotation of camshaft
34 about an axis substantially parallel to the tube causes fingers
42 to move sequentially in a direction substantially perpendicular
to the axis of camshaft 34. This moves fingers 42 in a wavelike
fashion to move I.V. solution 14 through tube 16 into patient
20.
The I.V. tube 16 can be placed in operation with peristaltic
mechansim 22 by location of respective fitments 58 and 60 into the
base 62 of peristaltic mechanism 22. As shown in FIG. 2, section 18
of I.V. tube 16 can be defined between fitment 58 and fitment 60.
This particular section 18 may be made of the same material as I.V.
tube 16. In the preferred embodiment, the section 18 comprises a
very flexible and compressible material, such as a silicon
rubber.
Once I.V. tube 16 and its associated pumping section 18 have been
mounted on peristaltic mechanism 22, a door 43 can be closed to
provide a platen 44 for supporting the tube 16 in substantially a
linear orientation. The platen 44 provides resistance against the
occluding movement of the fingers 42 as they sequentially urge on
section 18 of the I.V. tube 16. A membrane 54 may be interposed
between fingers 42 and tube section 18 to encase fingers 42
separately from pumping section 18 and to isolate I.V. tube 16 and
section 18 from the peristaltic mechanism 22. Camshaft rotation
angle .theta., and the helical orientation of appropriately shaped
cam lobes 40 along camshaft 34, cooperatively designate the timing
and amount of perpendicular movement of finger 42 along pumping
section 18. Further, it will be appreciated that each complete
revolution of camshaft 34 causes a complete cycle of sequential
movement of fingers 42 to urge against section 18 to generate a
peristaltic action of wavelike occlusion of the tube section
18.
OPERATION
In its operation, pump 10 is placed in operative engagment with an
I.V. tube 16. This is done by positioning I.V. tube 16 against base
62 of peristaltic mechanism 22 as shown in FIG. 2. With tube 16 in
its position, fitments 58 and 60 are operatively engaged with base
62. As discussed previously, the portion of I.V. tube 16 which is
placed against membrane 54 and in operative engagement with pump 10
is preferably a flexible and compressible tube section 18.
Once I.V. tube 16 and its section 18 have been engaged with pump
10, the door 43 is closed. The closure of door 43 causes platen 44
to contact section 18 and enclose section 18 between platen 44 and
membrane 54 for supporting the tube 16 in substantially a flat
linear orientation.
Activation of stepper motor 24 rotates drive shaft 26 causing drive
pulley 30 to rotate camshaft 34. The actual positioning of camshaft
34 is represented by camshaft rotation angle .theta.. Revolution of
camshaft 34 will cause the series of cam lobes 40 to reciprocate
fingers 42 in a direction substantially perpendicular to the axis
of section 18. Due to the helical configuration of cam lobes 40 on
camshaft 34, fingers 42 are sequentially urged against section 18
to create a moving zone of occlusion along the length of section 18
during revolution of camshaft 34.
During operation of peristaltic mechanism 22, as shown in FIG. 2,
rotation of camshaft 34 causes first finger 63 to occlude section
18 at point 64, and ultimate finger 70 to occlude at point 66. As
can be seen, simultaneous occlusion at points 64 and 66 creates a
pocket 78 within section 18 which is full of I.V. fluid 14. The
pressure in pocket 78 increases further as the rotating camshaft 34
causes second and third fingers 65 and 67 to be urged against
section 18. Ordinarily, if no pressure reduction mechanism is
provided, when ultimate finger 70 subsequently lifts off pumping
section 18, there will be a surge of fluid to patient 20. This
surge is caused by the pressure which has been allowed to build up
inside section 18. The present invention recognizes that the
pressure in pocket 78 may be reduced by increasing the rate at
which penultimate finger 68 and ultimate finger 70 are lifted off
from the tube 16.
As can be seen in FIG. 4A, when camshaft 34 rotates in the
direction of arrow 76, cam lobe 40 is correspondingly rotated
within aperture 56. Rotation of cam lobe 40 reciprocates finger 42
between an up or open position and a down or closed position with
respect to the center line of camshaft 34. The interaction between
each finger 42 and helically positioned cam lobe 40 causes the
fingers 42 to produce the reciprocal movement to sequentially urge
the fingers 42 against the section 18 for moving fluid through the
tube 16. Referring to FIG. 4B, the rate at which finger 68 is
lifted off from section 18 can be increased by modifying the shape
of penultimate cam lobe 72. Finger 68 can be lifted off of section
18 at a faster rate by providing a flat 69 which is integrally
formed on the circumference of penultimate cam lobe 72. As shown in
FIG. 4C, the rate of lift off of ultimate finger 70 can also be
increased by provided a flat 71 which is integrally formed on the
circumference of ultimate cam lobe 74. Flat 69 and flat 71 can be
configured to control the rates of lift off of penultimate finger
68 and ultimate finger 70, respectively, from pumping section
18.
To aid further in linearizing the flow of fluid to patient 20, the
amount of occlusion at point 66 may be reduced by shortening the
stroke length of ultimate finger 70, or by further modifying flat
71 of ultimate cam lobe 74. Preferably, the amount of occlusion is
modified by selectively forming the flat 71 of ultimate cam lobe 74
to shorten the reciprocal movement of the finger 70 in the
direction of the tube 16. Alternatively, ultimate finger 70 may be
shortened by approximately 1/100 of an inch as compared to the
uniform length of the remaining plurality of the fingers 42. These
modifications cause the occlusion time at point 66 to be reduced.
As can be seen in FIG. 4C, flat 71 of ultimate cam lobe 74 is
modified to displace the finger 70 such that its reciprocal
movement toward the section 18 is shorter than the movement of the
other fingers.
To further illustrate the interaction between fingers 42,
penultimate finger 68 and ultimate finger 70, a graph is shown in
FIG. 5 which illustrates the percent occlusion of each finger with
respect to time, with zero (0) percent representing fully open, and
one hundred (100) percent representing fully closed or fully
occluded. Initially, fingers 42, penultimate finger 68 and ultimate
finger 70 have identical rates of displacement against the section
18. This rate corresponds to a slope of line 80. As can be seen,
the normal rate of lift of (i.e. the rate at which a finger 42
would normally lift away from section 18) can be seen by slope 81
for line 82. In order to increase the rate of lift off, the cam
lobes 72 and 74 are modified to create a slope 83 for lines 84 and
86 which are steeper thus reflecting the increased rate of lift off
of penultimate finger 68 and ultimate finger 70 from tube 16. Thus,
penultimate finger 68 is lifted off section 18 more quickly, just
as second and third fingers 65 and 67 are urged against the section
18, reducing pressure which would otherwise be allowed to build up
in the pocket.
Still referring to FIG. 5, it can be seen also that the duration of
the occlusion of points 64 and 66 are different. Specifically,
occlusion point 66 has a relatively shorter occlusion time with
respect to occlusion point 64 due to modifying the cam lobe 74 as
previously discussed.
In sum, with the structure as described above, it is to be
appreciated that penultimate finger 68 is lifted at a faster rate
than fingers 42 in order to compensate for a possible build up in
fluid pressure when both points 64 and 66 are simultaneously
occluded. On the other hand, ultimate finger 70 is lifted at a
faster rate than fingers 42 in order to decrease occlusion time at
occlusion point 66 to thereby minimize the discontinuity in fluid
flow through tube section 18.
While the particular linear peristaltic pump with a pressure relief
mechanism as herein shown and disclosed in detail is fully capable
of obtaining the objects and providing the advantages herein before
stated, it is to be understood that it is merely illustrative of
the presently preferred embodiments of the invention and that no
limitations are intended to the details of construction or design
herein shown other than as defined in the appended claims.
* * * * *